Loudspeaker

A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A speaker system, also often simply referred to as a speaker or loudspeaker, comprises one or more such speaker drivers, an enclosure, and electrical connections possibly including a crossover network. The speaker driver can be viewed as a linear motor attached to a diaphragm which couples that motor's movement to motion of air, that is, sound. An audio signal, typically from a microphone, recording, or radio broadcast, is amplified electronically to a power level capable of driving that motor in order to reproduce the sound corresponding to the original unamplified electronic signal. This is thus the opposite function to the microphone; indeed the dynamic speaker driver, by far the most common type, is a linear motor in the same basic configuration as the dynamic microphone which uses such a motor in reverse, as a

Computational Analysis and Methods for Electromagnetic Exposure Limits, Antenna Optimization and Cell Phone Design

Chen Xi Lin

In recent years, the advancements of wireless technologies have led to rapid developments in the field of telecommunication, power delivery and bio-medical applications. During the evolution of a wireless technology, the electromagnetic compatibility (EMC) between a radiating source (e.g., an antenna) and nearby active or passive elements (e.g., a closely integrated electronic component or a human body) often introduces challenging design requirements. This thesis focuses on the applications of state-of-the-art computational electromagnetic compatibility (CEMC) techniques in multidisciplinary engineering design tasks, with an emphasis on computational bio-electromagnetic compatibility (CBEMC). The analyses reported in this thesis span practical applications from power frequency (Hz) to radio frequency (GHz), providing research outcomes which significantly benefit the understandings of low-frequency human body exposure safety and radio-frequency antenna integration and optimization. The research aspect of the thesis is initiated with a thorough review of the existing low-frequency exposure safety guidelines recommended by international regulatory committees. The subsequent analyses suggest essential scientific basis for the update and revision of the existing exposure limits. Practical exposure scenarios (e.g., magnetic resonant wireless power transfer) are investigated with novel assessment techniques. Subsequently, a computer-aided optimization scheme based on network-distributed genetic algorithms is applied to highly detailed numerical mobile phone model and human body phantoms. The investigated optimization technique is proven to be superior than traditional empirical approaches. Finally, the CEMC techniques are applied in the context of non-dosimetry related engineering design environment by investigating the integration of a miniature loudspeaker (acoustic component) and a mobile device antenna (radio frequency component). Based on simulation and measurement data, the coupling mechanisms are determined to establish the fundamental design guidelines for optimum antenna-speaker co-existence and performance. In summary, this thesis details several novel applications of CEMC in the most stringent and complex industrial design environments. The presented research findings serve as indispensable basis for future research oriented towards the exposure-compliant and electromagnetic- compatible designs for novel wireless technologies.

EPFL2013

Compensation des non-linéarités des systèmes haut-parleurs à pavillon

Delphine Bard

The assumptions of linearity and autonomy assumed in circuit theory are known to be respected only partially by electroacoustic transducers. In particular, the dynamics range of the latter is limited by the audible nonlinear effects that they are causing. In the domain of active noise control, the distortion products limit noise reduction performance. The present thesis work stems from characterization of these observations. We want to design a real-time system compensating the nonlinearities of electroacoustic devices. The first part of this report concerns the nonlinearity effects. It is shown that the use of classical characterization methods of an electroacoustic device (harmonic distortion, intermodulation, frequency difference ...) is limited. Hence, they can not be used to determine the nonlinearity laws themselves, but rather only their effects for arbitrary excitations. First, a method based on multitone harmonic excitations has been proposed and validated. It has been applied for the characterization of loudspeaker prototypes using several different technologies, which are used for active noise reduction in an aircraft turboreactor. The second part of this work addresses the elaboration and validation of a nonlinearity effect compensation method. This method is based on the description of the nonlinearities by the Volterra series. For this, we need to place an upstream system, characterized by the inverse nonlinearity law of the loudspeaker system. After having determined precisely the Volterra kernels of the system to be characterized, the kernels of the upstream compensation system are determined by assuming that their cascade obeys to a linear law. For this purpose, a kernel measurement method in the frequency domain has been developed, validated and tested. Since we are concerned with loudspeakers, we took their flying time into account. The compensation method has been validated by computing the simulated response of the compensation circuit. Resulting analog signals have then been applied to the loudspeaker. Measured performances fulfill the expectations. In the last part, the compensation method has been applied in a real-time Digital Signal Processing) DSP controller, which allowed to realize a demonstrator to the implemented for future industrial applications.

EPFL2005

Compensation des non-linéarités des systèmes haut-parleurs à pavillon

Delphine Bard

EPFL2005

Computational Analysis and Methods for Electromagnetic Exposure Limits, Antenna Optimization and Cell Phone Design

Chen Xi Lin

EPFL2013

Computational Analysis and Methods for Electromagnetic Exposure Limits, Antenna Optimization and Cell Phone Design

Compensation des non-linéarités des systèmes haut-parleurs à pavillon

Amplitude and phase synthesis of loudspeaker systems

Compensation des non-linéarités des systèmes haut-parleurs à pavillon

Amplitude and phase synthesis of loudspeaker systems

Computational Analysis and Methods for Electromagnetic Exposure Limits, Antenna Optimization and Cell Phone Design